In order to improve the processing speed of a semiconductor integrated circuit, it is necessary to achieve a low R/C time constant. Resistance R is lowered by using copper low in resistivity as wiring material, while electrostatic capacitance C is lowered by using an insulation film (low dielectric constant film) having a low dielectric constant K as an interlayer insulation film. Further, with the use of a low dielectric constant film, it is possible to prevent a crosstalk.
A porous insulation film enhanced in its rate of holes included is widely used as an insulation film having a low dielectric constant. However, a porous insulation film has a problem that it generally lacks strength and is highly hygroscopical due to its structure. Hence, many researches are made on a reforming method for hydrophobizing and strengthening the porous insulation film.
For example, the specification of U.S. Pat. No. 6,147,009 discloses a technique for forming an SiOC film by performing chemical vapor deposition (CVD) by plasma using 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS). However, there is a problem that it is difficult to form a film having an extremely low dielectric constant since porosity is hard to obtain if a CVD method is used.
A copper wiring is formed by forming a hard mask high in hardness and density on a low dielectric constant porous film by a damascene process, then performing etching by photolithography, and embedding a wiring in a groove formed by etching. The copper wiring is formed together with forming a barrier metal layer in the groove for preventing copper diffusion. However, in the porous film, the very barrier metal layer might be diffused. Unexamined Japanese Patent Application KOKAI Publication No. H9-298241 discloses providing a silicon oxide film to prevent diffusion of wiring materials into the porous film. Hereinafter, an insulation film having the same function as this silicon oxide film, i.e., capable of preventing diffusion of wiring materials (metals) will be referred to as sealing film.
According to a conventional film forming method, for reforming a porous film to further stack thereon an insulation film (a hard mask or a sealing film) different from the porous film in film property, the porous insulation film is reformed in a different chamber by using a different reaction substance, and another insulation film (a hard mask or a sealing film) is formed on the porous insulation film, resulting in a problem that the apparatus needs to be large in size and many process steps are involved.
A similar problem has been suffered also in a case where a low dielectric constant film, not only in case of it being a porous insulation film, is reformed to form thereon another insulation film (a hard mask, a sealing film, or a passivation film), etc. having a different film property.